Access to eBooks is limited to institutions that have purchased or currently subscribe to the SPIE eBooks program. eBooks are not available via an individual subscription. SPIE books (print and digital) may be purchased individually on SPIE.Org.

Contact your librarian to recommend SPIE eBooks for your organization.
Chapter 8:
Confronting the Diffraction Limit
Abstract
As k 1 factors [Eq. (2.8)] fall below 0.8, a number of effects become observable that are not seen when k 1 is larger. Processes with small values of k 1 began to appear in the mid-1990s, and are quite common today, as seen from Table 8.1. Some of the effects seen in patterns generated with low-k 1 processes are discussed in this chapter. Several techniques also described—such as off-axis illumination and phase-shifting masks—have been developed to address the shortcomings of optical imaging as feature sizes become smaller than the wavelength of light. Methods to improve image contrast that involve modification of the mask or illumination are referred to collectively as resolution enhancement techniques (RETs) and are discussed in this chapter. 8.1 Off-axis illumination As discussed earlier, light (coherent) that illuminates a grating is diffracted in very specific directions [Eq. (2.1)]. For normally incident light, sufficiently small dimensions result in situations where all beams except the zero-order are diffracted outside the entrance pupil of the imaging optics (Fig. 8.1). In this case, no pattern is formed, because a single beam is a plane wave, containing no spatial information, as explained in Chapter 2. For normally incident (“on-axis”) illumination, the grating is not imaged when the pitch is too small, because only a single beam, the zero-order beam, is transmitted through the lens. This illustrates the limitation to resolution imposed by diffraction.
Online access to SPIE eBooks is limited to subscribing institutions.
CHAPTER 8


SHARE
Back to Top